1. Field of the Invention
The instant invention relates to the formation of a protective coating on a siliceous substrate through the use of an alkoxy silane to provide a weather-resistant, easily cleaned surface, and specifically relates to the mechanized application of such coatings.
2. State of the Art
Various silane formulations and compositions have been used to provide various types of coatings upon glass or other vitreous or siliceous surfaces. In U.S. Pat. No. 3,244,541 (Fain et al.), a dimethyl diethoxy silane is disclosed as one which in conjunction with a minute amount of sulfuric acid readily forms a protective coating on a vitreous surface.
In U.S. Pat. No. 3,442,664 a polymeric fluorine-containing, hydrolytically-stable organo siloxane having a viscosity from 500 to 500,000 centipoise is utilized as a coating composition. Earlier patents such as those to Stedman (U.S. Pat. No. 2,923,653 and U.S. Pat. No. 2,612,458) and Fain (U.S. Pat. No. 2,962,390) describe various silane wax compositions. The composition utilized in Fain et al. (U.S. Pat. No. 3,244,541) is stated to form a transparent coating but that if a significant amount of sulfuric acid, for example above 0.75% by weight is utilized, the coating is "greasy." Apparently unknown to Fain, it has been discovered that this greasiness also occurs with formulations containing less acid under varying conditions of humidity, temperature and time.
The work of Fain et al. does not describe the various humidity conditions under which the coating compositions of Fain et al. were applied. It has been discovered that at high humidity, the problem of a greasy film is much less likely to occur. The work of Fain et al., if it was done in New York where the headquarters of the corporation to which the patent is assigned is located, results in coatings which would generally have been applied in relatively high humidity conditions.
It has recently been found that there is less problem in obtaining a useful film during application in high humidity conditions. However, application of compositions of Fain et al. in low humidity applications results in greasy films. This greasiness is extremely difficult to remove and the greasy appearance is unacceptable in a coating for glass substrates in which good optical properties are necessary and desired. Thus, windows of buildings cannot be properly coated unless this greasy condition is prevented from occurring.
The formation of non-greasy coatings must be obtainable with every application of a protective coating if a coating system is to be useful in outdoor and indoor environments where conditions of humidity and temperature vary. In most situations, humidity control is not possible during the coating process and may vary during the course of a day or several days where all the windows of a large building, for example, are being coated.
The application of protective coatings in varying conditions of humidity and temperature in a manner which avoids the creation of a greasy film requires the monitoring and detection of the end of the reaction and a removal of excess coating material before significant homopolymerization occurs to cause a greasy film. This aspect of the process was disclosed in the previous application from which this application is a continuation-in-part. The means for detecting the end point of the reaction and the removal of excess coating material was disclosed for small-scale processing of siliceous or vitreous substrates. However, industrial applications require the ability to process and coat large sizes and amounts of glass which, in itself, requires methods and apparatus for quickly and properly coating siliceous or vitreous substrates.